This invention relates to a process for preparing dispersions of copolymers in polyahls and to the resulting copolymer dispersions and polyurethane products.
Polyurethanes constitute a broad class of polymeric materials having a wide range of physical characteristics. The polymers are produced by the reaction of a polyisocyanate with a polyfunctional compound having an active hydrogen in its structure. This active hydrogen compound is generally a liquid or solid capable of being melted at relatively low temperatures. Most commonly, the active hydrogen compound contains hydroxyl groups as the moieties having the active hydrogen and thus are termed polyols, e.g., the polyols of polyesters, polyester amides, or polyethers, or mixtures of two or more such materials. For reasons of commercial availability and cost, the polyols most commonly employed in the preparation of polyurethanes are the polyethers having hydroxyl terminated chains and hydroxyl terminated polyesters.
Although a wide variety of physical and chemical properties are obtainable by the proper selection of a polyisocyanate and the polyol as well as the conditions under which the polyurethane reaction is carried out, the resulting polyurethane often exhibits properties, e.g., load bearing and processability, which are unacceptable for some applications, particularly for foam applications as well as for elastomer and plastic applications.
To improve such properties, it has been the practice of the art to employ graft copolymer dispersions (often called polymer polyols) prepared from vinyl monomers and polyols in the preparation of polyurethanes as shown in U.S. Pat. Nos. 3,383,351; 3,304,273; 3,523,093; 3,652,639 and 3,823,201. In U.S. Pat. No. 3,304,273, a mixture of styrene and a polar monomer are copolymerized while dispersed in a polyol which is essentially free of ethylenic unsaturation. Unfortunately, stable dispersions cannot be prepared by this technique if high proportions of styrene monomer are employed. Subsequently, in order to overcome this problem, it was found desirable to employ polyols which contain a significant amount of ethylenic unsaturation. For example, as stated in U.S. Pat. No. 3,823,201, to Pizzini et al.,
" . . . the stability of dispersions obtained by the in situ polymerization of vinyl monomers in polyols is a result of the formation of surface stabilizing species. Without a stabilizing species which provides a repulsive barrier between the polymer particles, the polymerized material will agglomerate and form irregularly shaped lumps . . . the stabilizer is an amphipathic polymer consisting of lyophobic vinyl polymer and lyophilic polyether chains. The vinyl polymer part is absorbed and/or chemically built in the particle surface while the polyether part reaches out in the surrounding polyol phase providing a protective shield against coagulation." PA1 (A) a polyahl having a number average molecular weight less than 400 and dispersed therein; and PA1 (B) an addition copolymerizate of (1) the adduct of the monoahl and the active ethylenically unsaturated coreactant (hereinafter called "coreactant monomer") and (2) at least one ethylenically unsaturated monomer other than a coreactant monomer (hereinafter called "other monomer"); or PA1 (C) a mixture of (1) an adduct of (i) the monoahl and (ii) an addition copolymer of the coreactant monomer with at least one "other monomer" which is nonreactive with the coreactive moiety of the coreactant monomer and the monoahl and (2) an ethylenic addition polymer of at least one "other monomer"; or PA1 (D) a combination of (B) and (C); or PA1 (E) a combination of (B) and/or (C) and a polymer of at least one "other monomer", said monoahl and coreactant monomer being present in reacted form in an amount sufficient to stabilize the dispersion.
Although it is desirable to have some unsaturation in the polyol, it has been found (e.g., U.S. Pat. No. 3,652,639 to Pizzini et al.) that larger mole ratios of unsaturation to polyol such as 1:1 to 3:1 cause unacceptably high viscosities in the resultant dispersions.
Accordingly, it is highly desirable to provide a nonaqueous copolymer dispersion exhibiting increased stability and reduced viscosities.